The present invention relates generally to gas turbine engines, and, more specifically, to reduction of exhaust noise.
A typical gas turbine engine includes a compressor for pressurizing air which is mixed with fuel and ignited in a combustor for generating hot combustion gases which flow through one or more stages of turbines that power the compressor in a core engine configuration. Typically cooperating with the core engine is a low pressure compressor, such as a fan, disposed upstream of the high pressure compressor of the core engine, which is powered by a low pressure turbine disposed downstream from the high pressure turbine of the core engine.
In a typical turbofan aircraft gas turbine engine application for powering an aircraft in flight, a core exhaust nozzle is used for independently discharging the core exhaust gases inside a concentric fan exhaust nozzle which discharges the fan air therefrom for producing thrust. The separate exhausts from the core nozzle and the fan nozzle are high velocity jets typically having maximum velocity during take-off operation of the aircraft with the engine operated under relatively high power. The high velocity jets interact with each other as well as with the ambient air and produce substantial noise along the take-off path of the aircraft.
U.S. Pat. No. 6,360,528, assigned to the present assignee, discloses an improved exhaust nozzle including a row of chevrons which promote mixing of exhaust flow for noise attenuation. The chevrons are triangular and extend from an aft end of an exhaust duct and define complementary diverging slots circumferentially or laterally therebetween. The chevrons are integral extensions of the exhaust duct, and are preferably coextensive with the outer and inner surfaces thereof.
In a typical annular exhaust duct, the inner surface thereof is circumferentially concave, and the inner surfaces of the row of chevrons are correspondingly circumferentially concave. However, by introducing an axially concave component of curvature in the radially inner surfaces of the chevrons, each chevron may therefore have a compound shallow bowl therein for enhancing performance.
These shallow bowl triangular chevrons have been built, tested, and are found in commercially available engines for powering aircraft in flight. In a typical turbofan engine application, the chevron exhaust nozzle replaces the otherwise simple annular core exhaust nozzle and effects substantial noise attenuation as the core exhaust gases mix with the fan exhaust flow channeled thereover during operation.
However, noise attenuation comes with a corresponding price. In particular, the chevron exhaust nozzle introduces additional pressure losses in the exhaust flows being mixed thereby which decreases the overall efficiency or performance of the engine. In an aircraft engine application, more fuel is required to power the aircraft than would be otherwise required with a conventional circumferentially continuous exhaust nozzle having a plain circular outlet.
Accordingly, it is desired to provide a chevron exhaust nozzle having improved performance for reducing fuel consumption during operation.